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2.2 Measuring Earthquakes

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Vocabulary

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Focus: is the point beneath earth's surface where rocks that are under stress break, triggering an earthquake
Epicenter: the point on the surface directly above the focus
Seismic waves: the vibrations that travel through Earth carrying the energy released during an earthquake
P waves: earthquakes waves that compress and expand the ground like an accordion
S waves: earthquakes waves that vibrate from side to side as well as up and down
Surface waves: when P waves and S waves reach the surface, some of them become surface waves
Seismograph: records the ground movements caused by seismic waves as they move through earth
Magnitude: is a measurement of earthquake strength based on seismic waves and the movement along the faults
Mercalli scale: was developed to rate earthquakes according to their intensity
Richter scale: is a rating of size of seismic waves as measured by a particular type of mechanical seismograph
Moment magnitude scale: a rating system that estimates the total energy released by an earthquake

Outline

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Seismic Waves

• Primary waves
  • P Waves
    • compress and expand the ground
• Secondary Waves
  • S Waves
    • they vibrate from side to side and up and down
• Surface Waves
  • it moves more slowly than S waves and P waves
  • it causes most severe damage

Detecting Seismic Waves

• geologists use seismographs to detect seismic waves

Measuring Earthquakes

• geologists study the magnitude of all earthquakes
• Mercalli Scale
  • it rates earthquakes according to their intensity
• Richter Scale
  • rates size of seismic waves as measured by a particular type of mechanical seismograph
• Moment Magnitude Scale
  • estimates total energy released by an earthquake

Locating the Epicenter

• geologists use seismic waves to locate the epicenter